## Friday, August 15, 2008

### Wireless electricity

I was sent an interesting article yesterday about Atlantis. Most of this article is, as I call it, "conspiracy theories" - the most hilarious part is where the author claims that a mountain in Canada was shaped to resemble a head of an Indian. There is indeed such mountain, it was discovered by the users of Google earth. However, I really fail to see any reason to believe that this was done by humans and not by wind. I am so skeptical because if we assume that it was indeed build be someone, we get an even harder question: Why was it built? Constructions of this size are not built without a purpose, and I don't see any purpose to this one. It is not even art, since it can be viewed only from the air. The article in question also doesn't answer this.

Wireless power
Is it possible to power a device without wires? Of course it is. While working on his project Tesla build a room in which lamps (florescent) started to work even when not connected to the power outlets. This is based on the Faraday law - if we have a changing magnetic field we will get voltage. Tesla created a strong, constantly changing electromagnetic field in his room which powered his florescent lamp. There is no fiction in this, this principal is well known and is used on a daily basis - this is exactly how radio works. In a radio station, we have a transmitter that sends a changing electromagnetic wave in space, and this wave creates voltage on the radio antenna. in reality, this is slightly more complicated, but I don't want to get into the detailt of how a radio works.
Another way to transfer power without wires is to use displacement currents. This method was also known to Tesla, but it requires one wire so it is not exactly wireless.

Is it dangerous
From the above paragraph it is clear that if we want wireless power what we need is to create a strong electromagnetic field. Will such field have negative influence on people/other objects?
The answer to this is no and yes. People are not harmed by magnetic fields. The reason to this is that such fields influence only charges in motion or paramagnetic materials. Our bodies don't have any charge, and organic tissue is not paramagnetic. But, a computer in such a field would be fried immediately. The reason to this is that such field would not only supply power, it would effect all the circuits in the computer, and this would simply destroy them, probably with a little fire. It is possible to create a defense against such fields, there are materials which can block an electromagnetic field. But such a defense will have to be large and heavy.

Can it be done
So, we know that it is possible to transmit power without wires and we know how to protect computers and other gentle electronics from it. But can we use it? No. The reason for this is very simple. It is not a problem to create a strong magnetic field, but such fields become much less stronger with the distance. To be precise, the electromagnetic field drops as the square of the distance from the source. To bring some perspective, lets suppose that we have a field of 1000 Tesla. After what distance it will be only as strong as the field of the magnet you put on your refrigerator? The equation we get is:

$\frac{1000}{x^2}=0.1$

And the solution is 100. This means that after 100 meters from the power source the field will be very small. But this is only a 1000 Tesla, right? So if we will take more it will be fine. Unfortunately, no. Tesla is a very large unit. It is simply impossible with current technologies to create magnetic fields so strong. The strongest steady magnet created until now is under 45 Tesla. Also, even if we will be capable of creating electromagnetic fields strong enough, such fields will also cause little pieces of iron to fly to the magnet like a bullet. Besides, think about all the power loses.
Because of the above mentioned problems, it is practically impossible to operate a city on such wireless power source. However, the method I discussed is only a simplified version of what Tesla wanted to build.

Was Tesla wrong?
Surprisingly, no. I am sure that all the points I mentioned above were known to him. However, he found a way to solve this problem. I am not going to describe his idea in detail, but basically the plan was to use the resonance frequency of the earth and the ionosphere as a conduction layer. Tesla even claimed that he was able to transmit power across 25 miles with only 5% power loss. So, theoretically it is indeed possible that a civilization that is described in the article existed and used such power source.